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Gabriel Aullón

Publications and source records attributed to Gabriel Aullón.

11 recordsLinked to original sources
PubMed2007

Chelating dialkoxide titanium complex: a versatile building block for the construction of heterometallic derivatives.

The heterometallic complex [TiCp*(O(2)Bz)(2)AlMe(2)] (2) has been synthesised by reaction of [TiCp*(O(2)Bz)(OBzOH)] (1) with AlMe(3) (Cp*=eta(5)-C(5)Me(5); Bz=benzyl). Complex 1 reacts with HOTf to yield the cationic derivative [TiCp*(OBzOH)(2)]OTf (3) (HOTf=HSO(3)CF(3)). Compound 3 reacts with [{M(mu-OH)(cod)}(2)] (M=Rh, Ir; cod=cyclooctadiene) to render the early-late heterometallic complexes [TiCp*(O(2)Bz)(2){M(cod)}(2)]OTf (M=Rh (4); Ir (5)). The molecular structure of complex 4 has been established by single-crystal X-ray diffraction studies.

Journal Article↗
PubMed2006

Isomeric distribution and catalyzed isomerization of cobalt(III) complexes with pentadentate macrocyclic ligands. importance of hydrogen bonding.

We have investigated the isomeric distribution and rearrangement of complexes of the type [CoXLn]2+,3+ (where X = Cl-, OH-, H2O, and Ln represents a pentadentate 13-, 14-, and 15-membered tetra-aza or diaza-dithia (N4 or N2S2) macrocycle bearing a pendant primary amine). The preparative procedures for chloro complexes produced almost exclusively kinetically preferred cis isomers (where the pendant primary amine is cis to the chloro ligand) that can be separated by careful cation-exchange chromatography. For L13 and L14 the so-called cis-V isomer is isolated as the kinetic product, and for L15 the cis-VI form (an N-based diastereomer) is the preferred, while for the L14(S) complex both cis-V and trans-I forms are obtained. All these complexes rearrange to form stable trans isomers in which the pendent primary amine is trans to the monodentate aqua or hydroxo ligand, depending on pH and the workup procedure. In total 11 different complexes have been studied. From these, two different trans isomers of [CoClL14(S)]2+ have been characterized crystallographically for the first time in addition to a new structure of cis-V-[CoClL14(S)]2+; all were isolated as their chloride perchlorate salts. Two additional isomers have been identified and characterized by NMR as reaction intermediates. The remaining seven forms correspond to the complexes already known, produced in preparative procedures. The kinetic, thermal, and baric activation parameters for all the isomerization reactions have been determined and involve large activation enthalpies and positive volumes of activation. Activation entropies indicate a very important degree of hydrogen bonding in the reactivity of the complexes, confirmed by density functional theory studies on the stability of the different isomeric forms. The isomerization processes are not simple and even some unstable intermediates have been detected and characterized as part of the above-mentioned 11 forms of the complexes. A common reaction mechanism for the isomerization reactions has been proposed for all the complexes derived from the observed kinetic and solution behavior.

Journal Article↗
PubMed2006

Effects of tris(pyrazolyl)borato ligand substituents on dioxygen activation and stabilization by copper compounds.

Dinuclear [Cu2(mu-O)2(Tp(R,R')2] complexes, analogues of the active site of oxyhemocyanin, are theoretically studied, and the effect of the substituents of the tris(pyrazolyl)borate ligands, Tp(R,R'), is analyzed. Density functional theory calculations reveal that the type of bridging oxygen, peroxo, or bisoxo is strongly influenced by the nature and position of the R substituents because of variable substituent...bridging oxygen interactions, as well as electronic effects. The electronic effects of ligands at the 5 position are not significant, but peroxo complexes are favored by electron-withdrawing groups at the 3 position while bisoxo ones are strongly sterically disfavored.

Binding Sites↗
PubMed2005

A pyrimidine thiolate Rh(I) complex: structure, bonding and one-dimensional interactions in solid and in solution.

The reaction of [Rh(micro-Cl)(COD)]2 with 4,6-dimethyl-pyrimidinethiolate (Me2-pymt) and subsequent substitution of COD by CO yields [Rh(Me2-pymt)(CO)2]. The stacking pattern found in this compound is in contradiction with previously studied comparable square-planar complexes of type d8-[M(chelate)(monodentate)2] in which each ligand has different pi-acidic character. A theoretical study of the intermolecular interactions and conformation of the title compound has been carried out, combining semi-empirical band calculations on the real chains and ab initio(MP2 level) calculations on a model dimer. The combination of electronic and steric effects determines the rotation of the successive monomers and the deviation from linearity of the one-dimensional stacks. Its behaviour in solution is also special, developing a blue colour and forming micelles, when adding water to acetone solutions.

Journal Article↗
PubMed2004

Chalcogen-chalcogen bonds in edge-sharing square-planar d8 complexes. Are they possible?

A theoretical study of the formation of X-X bonds in complexes with the general formula [M(2)(mu-X)(2)L(4)] (M = group 10 and X = group 16 elements) having d(8) transition-metal atoms is presented. The existence of two energy minima for some complexes, with short and long X-X distances, is shown by density functional theory calculations, and the factors responsible for it are analyzed, including a strong influence of the nature of the metals and ligands on the relative stability of the two isomers. The influence of the bite angle of chelating terminal ligands and the nature of the donor atom on the relative stabilities of the two isomers are also discussed.

Journal Article↗
PubMed2004

A new class of (mu-eta2:eta2-disulfido)dicopper complexes: synthesis, characterization, and disulfido exchange.

Rare examples of (mu-eta2:eta2-disulfido)dicopper complexes have been prepared from Cu(I) and Cu(II) complexes of beta-diketiminate and anilido-imine supporting ligands. A novel byproduct derived from sulfur functionalization of the methine position of a beta-diketiminate ligand was identified. DFT calculations on [(LCu)2X2] (L = beta-diketiminate, X = O or S) complexes rationalize the absence of a bis(mu-sulfido)dicopper isomer, [Cu2(mu-S)2](2+), in the synthetic reactions, yet predict that a [Cu2(mu-S)2](0) core is a stable product of 2-electron reduction of the [Cu2(mu-eta2:eta2-S2)](2+) unit. Exchange of the disulfido ligand was discovered upon reaction of a (mu-eta2:eta2-disulfido)dicopper complex with a Cu(I) reagent.

Copper↗
PubMed2003

The evolution of [[Ph2P(CH2)nPPh2]Pt(mu-S)2Pt[Ph2P(CH2)nPPh2]] (n=2, 3) metalloligands in protic acids: a cascade of sequential reactions.

Given the nucleophilicity of the [Pt(2)S(2)] ring, the evolution of [Pt(2)(mu-S)(2)(P intersection P)(2)] (P intersection P=1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp)) metalloligands in the presence of the simplest electrophilic species, the proton, has been studied. Combined use of experimental and theoretical data has allowed the whole set of reactions ensuing the protonation of the [Pt(2)S(2)] core to be established. The titration of [Pt(2)(mu-S)(2)(P intersection P)(2)] with HCl or HClO(4) was monitored mainly by (31)P[(1)H] NMR and mass techniques. Characterization of all the species involved was completed with the determination of the crystal structure of [Pt(SH)(2)(P intersection P)], for dppe and dppp, and [Pt(3)(mu(3)-S)(2)(dppp)(3)](PF(6))(2). The first protonation step of the [Pt(2)S(2)] core leads to the stable [Pt(2)(mu-S)(mu-SH)(P intersection P)(2)](+) complex, but the second step implies disintegration of the ring, thus giving rise to various mononuclear species. The subsequent evolution of some of these species allows regeneration of [Pt(2)(mu-S)(mu-SH)(P intersection P)(2)](+), evidencing the cyclic nature of this process. Whereas the reaction pathway is essentially common for both phosphine ligands, dppe and dppp, the different coordinating ability of Cl(-) or ClO(4) (-) determines the nature of the final products, [PtCl(2)(P intersection P)], [Pt(3)(mu(3)-S)(2)(P intersection P)(3)]Cl(2) or [Pt(3)(mu(3)-S)(2)(P intersection P)(3)](ClO(4))(2). DFT calculations have corroborated the thermodynamic feasibility of the reactions proposed on the basis of experimental data.

Journal Article↗
PubMed2002

Theoretical clues to the mechanism of dioxygen formation at the oxygen-evolving complex of photosystem II.

The mechanism of the generation of dioxygen at the oxygen-evolving complex (OEC) of photosystem II (PSII), a crucial step in photosynthesis, is still under debate. The simplest unit present in the OEC that can produce O2 is a dinuclear oxo-bridge manganese complex within the tetranuclear Mn4 cluster. In this paper we report a theoretical study of the model complexes [Mn2(mu-O)2(NH3)6(H2O)2]n+ (n = 2-5), for which density functional calculations have been carried out for several electronic configurations. The molecular orbital picture deduced from the calculations indicates that one-electron oxidation of the Mn2IV,IV/(O2-)2 complex (n = 4) mostly affects the oxygen atoms, thus ruling out the existence of a MnV oxidation state in this context, while the incipient formation of an O-O bond in the O2(3-) transient species evolves exothermally toward the dissociation of dioxygen and a Mn2II,III couple. These results identify the electronic features that could be needed to enable an intramolecular mechanism of oxygen-oxygen bond formation to exist at the OEC during photosynthesis.

Electron Transport↗
PubMed1996

On the Existence of a Pyramidality Effect in d(8).d(8) Contacts. Theoretical Study and Structural Correlation.

A qualitative molecular orbital study of d(8).d(8) contacts, using as models the dimers of [RhCl(CO)(3)] and cis-[PtCl(2)(CO)(2)], is presented, focusing on the effect of the pyramidalization of the metal atom on the strength of the metal-metal interaction. The existence of a pyramidality effect in dimers of d(8)-ML(4) complexes is supported also by the results of ab initio MP2 calculations on the dimer of cis-[PtCl(2)(CO)(2)]. A structural database analysis shows that a correlation between the pyramidality and the M.M distance exists for several families of dimers, oligomers, and polymers of square planar complexes of Ni(II), Pd(II), Pt(II), and Au(III). The importance of the pyramidality effect in those compounds is discussed in comparison with similar effects in binuclear complexes with metal-metal bonds of different multiplicities.

Journal Article↗
PubMed1996

Axial Bonding Capabilities of Square Planar d(8)-ML(4) Complexes. Theoretical Study and Structural Correlations.

A qualitative molecular orbital study and a structural analysis of the bonding capabilities of the metal atoms in square planar ML(4) complexes of d(8) ions are presented. In addition to analyzing the donor-acceptor properties of the metal atom in such complexes, the following aspects are also studied: (a) the effect of axial groups (bases or acids) on the donor-acceptor properties of the metal atom; (b) the effect of the axial groups on the deviation of the ML(4) ensemble from planarity; (c) the effect of an axial group on the bond between the metal atom and another group in trans; and (d) the implications on chemical reactivity.

Journal Article↗